Low current heaterless hollow cathode neutralizer for plasma propulsion—Development overview

Abstract

Hollow cathodes serve as electron sources for the operation of electric thrusters aboard spacecraft. Conventionally, hollow cathodes utilize a heating element to raise the temperature of the electron emitting material embedded in the cathode. To simplify cathode design and operation, in recent years, heaterless cathode technology has been under development in various facilities around the world. This paper overviews the development of a low current heaterless hollow cathode, designed and produced by Rafael, and denoted the ARC-1A. The ARC-1A generates a discharge current of 0.3–1.2 A and is ignited using breakdown voltages below 400 V. Each of the development phases is elaborated upon. These phases included activities such as a technology study, the development of manufacturing processes, the study of failure modes, and performance characterization and culminated with two primary tests—a 5000 h endurance test and a 3500 cold ignition cycles test. In its current state of development, the ARC-1A proves suitable for a wide range of low power electric thrusters and was successfully coupled with two different Hall effect thrusters in a wide range of low discharge current levels (0.5–1.1 A).

Ionization instability and turbulence in the plume of sub-ampere hollow cathodes with applied magnetic field

“…Here, the discharge potential at I a = 0.5 A is larger than in conventional orificed low-current cathodes [26], i.e. typically < 40 V, but unsurprisingly high for an open-end emitter cathode operating at such low mass flow rate [44,45].…”

Perspectives, frontiers, and new horizons for plasma-based space electric propulsion

“…107,108 In recent years, HHCs have seen an increased interest, specifically for low current hollow cathodes. 109,110,111,112,113,114 The quick ignition time, low power demand during the ignition phase, and the potentially longer lifetime have made these cathodes attractive options for low power ion and Hall thrusters. To date, the HHC technology has overcome two technological challenges: the ignition voltage is reduced to merely several hundred volts, 104 and the transition to operational temperature of the insert is with minimal damage to the cathode, thus allowing for thousands of ignitions.…”

“…To date, the HHC technology has overcome two technological challenges: the ignition voltage is reduced to merely several hundred volts, 104 and the transition to operational temperature of the insert is with minimal damage to the cathode, thus allowing for thousands of ignitions. 114 Further, it was shown that low-power HHCs can operate adequately with different insert materials such as the electride C12A7e-, 110,111 BaO-impregnated tungsten, 113,114,115 and LaB6. 112,113 Nevertheless, the current HHC technology development still needs to overcome two leading challenges: 1) Cathode Conditioning: after exposure to ambient air the insert must be conditioned, that is gradually heated to emit impurities.…”

Discharge and plasma plume characterization of a 100 A-class LaB6 hollow cathode

“…Moreover, in the case of Hall thrusters, electrons generated by the cathode also play a key role in ion production and plasma discharge sustainment [7,8]. The hollow cathode technology has greatly evolved and improved over the past decades thanks to advances in material science, manufacture processes and numerical simulations as explained in several articles [8][9][10][11][12]. Available cathodes are stable and efficient, have a long lifespan and are able to operate in a wide range of discharge currents from less than 1 A up to several tens of Amperes.…”